The present invention relates to a posture control system of a legged mobile robot, and specifically to a system for ensuring that a legged mobile robot, in particular a biped walking robot, reserves dynamic balance to maintain a stable posture, even when the robot is subject to unexpected object reaction force. More specifically, the present invention is most effectively applicable in a legged mobile robot having arms, and coordinately controls the arms and legs of the robot.
It should be noted that in this specification the term xe2x80x9cobject reaction forcexe2x80x9d is used to indicate the external force acting on the robot in a working environment including an object with which the robot is working, but excluding the floor reaction force acting on the robot from the contacting floor.
A legged mobile robot, in particular a biped walking robot having arms, is known from, for example, xe2x80x9cDevelopment of a Biped Walking Robot Compensating for Three-Axis Moment by Trunk Motionxe2x80x9d in vol. 11. No. 4, May 1993; xe2x80x9cJournal of the Robotics Society of Japanxe2x80x9d. The robot is provided with balance weights in the form of simplified arms. A desired gait is designed in advance using variables including anticipated gravity and inertial force to be generated by swinging the balance weights and robot walking is controlled to follow the designed gait.
In the prior art, however, the control is based on the premise that the arms are subject to no object reaction force. Therefore, if the control disclosed in the prior art is applied not only to walking, but also to working, the robot would be likely to lose dynamic balance, if it is subject to unexpected object reaction force from an object, resulting in the posture becoming unstable or, at worst, tipping over.
The applicant discloses a similar legged mobile robot in Japanese Laid-open Patent Application No. Hei 7 (1995)-205069 and proposes forcibly swinging robot arms to restore posture stability when the frictional force on the contact floor drops during walking.
In the control of legged mobile robot proposed therein by the applicant, however, the legs and arms are not controlled coordinately, but are separately or independently controlled. As a result, the robot may sometime lose dynamic balance due to the resultant force comprised of the force of gravity and inertial force generated by the arm swinging and reaction force from an object, thereby, contrary to what is expected, falling into an unstable posture.
A first object of the present invention is to solve the drawbacks of the prior art and to provide a posture control system for a legged mobile robot which can ensure to reserve dynamic balance or equilibrium so as to maintain a stable posture even when the legged mobile robot is subject to unexpected object reaction force.
A second object of the present invention is to provide a posture control system for a legged mobile robot which can effectively prevent the robot from tilting or tipping, even when the object reaction force changes abruptly, by displacing the position of center of gravity of the robot to a position at which the force is statically balanced.
A third object of the present invention is to provide a posture control system for a legged mobile robot which can maintain dynamic balance or equilibrium by properly changing the position of center of gravity of the robot and the floor reaction force even under a transit during which the displacement of position of center of gravity of the robot is in progress in response to the abrupt change of the object reaction force.
A fourth object of the present invention is to provide a posture control system for a legged mobile robot with arms which can reserve dynamic balance or equilibrium so as to maintain a stable posture, even when the robot arm is subject to unexpected gravity and inertial force or unexpected object reaction force when the robot arm is moved in a motion pattern not anticipated beforehand.
In order to achieve the above-mentioned objects, the present invention is configured to have a system for controlling posture of a legged mobile robot having at least a body and a plurality of links each connected to the body, comprising: desired gait predetermining means for predetermining a desired gait of the robot including at least a motion pattern including at least a desired trajectory of the body of the robot, a desired trajectory of floor reaction force acting on the robot, and a desired trajectory of external force other than the floor reaction force, acting on the robot; external force detecting means for detecting the external force other than the floor reaction force; external force difference determining means for determining an external force difference between the detected external force other than the floor reaction force and the external force of the desired trajectory; a model expressing a relationship between perturbation of the floor reaction force and perturbation of at least one of a position of center of gravity and a position of the body of the robot; model input amount determining means for determining a model input amount to be inputted to the model based on at least the determined external force difference; desired body trajectory correcting amount determining means for operating to input the model input amount to the model and based on a perturbation amount of at least one of the position of center of gravity and the position of the body obtained therefrom, for determining a desired body trajectory correcting amount, which corrects the desired trajectory of the body; desired floor reaction force trajectory correcting amount determining means for determining a desired floor reaction force trajectory correcting amount, which corrects the desired trajectory of the floor reaction force, based on at least the determined model input amount; and joint displacing means for displacing joints of the robot based on at least the determined desired body trajectory correcting amount and the desired floor reaction force trajectory correcting amount.
It should be noted here that the xe2x80x9cpositionxe2x80x9d is used to indicate, except for the position of gravity, the xe2x80x9cposition and/or posturexe2x80x9d. The xe2x80x9cposturexe2x80x9d indicates the orientation or direction in the three-dimensional space as will be stated later.
It should be noted here that the xe2x80x9cdesired trajectory of floor reaction forcexe2x80x9d is used to indicate, more specifically, a desired trajectory of a central point of floor reaction force. It should also be noted that xe2x80x9ccorrects the desired trajectory of the floor reaction forcexe2x80x9d is used to indicate, more specifically, correction of the moment about the central point of floor reaction force.
It should further be noted here that xe2x80x9cdetecting the external forcexe2x80x9d is used to mean not only to detect, but also to estimate with the use of a disturbance observer.
It is configured in the system, the model input amount determining means includes: equilibrium center of gravity position perturbation amount determining means for determining a perturbation amount of an equilibrium position of the center of gravity at which the external force is statically balanced; and wherein the model input amount determining means determines the model input amount such the model converges to the perturbation amount of equilibrium position of the center of gravity.
It is configured in the system, the model is a model which approximates the robot by an inverted pendulum.
It is configured in the system, the equilibrium center of gravity position perturbation amount determining means includes: a limiter which limits the determined perturbation amount of equilibrium position of center of gravity within a predetermining range.
It is configured in the system, the desired floor reaction force trajectory correcting amount determining means includes: a limiter which limits the determined desired floor reaction force trajectory correcting amount within a predetermined range.
It is configured in the system, the desired trajectory of the floor reaction force includes at least a desired trajectory of a central point of the floor reaction force acting on the robot.
It is configured in the system, the desired floor reaction force trajectory correcting amount determining means determines the desired floor reaction force trajectory correcting amount such that the desired floor reaction force trajectory correcting amount is equal to a difference obtained by subtracting the external force difference from the model input amount.
It is configured in the system, the external force other than the floor reaction force is a reaction force acting on the robot from an object through the links.
It is configured in the system, the robot is a legged mobile robot having two leg links and two arm links each connected to the body.
The present invention is further configured to have a system for controlling a posture of a legged mobile robot having at least a body and a plurality of links each connected to the body, comprising: desired gait predetermining means for predetermining desired gait of the robot including at least a motion pattern including at least a desired position of the body of the robot and a trajectory of a desired central point of floor reaction force acting on the robot; object reaction force detecting means for detecting an object reaction force acting on the robot from an object through the links; object reaction force moment converting means for converting or transforming the detected object reaction force into a moment about the desired central point of the floor reaction force; robot position/posture correcting means for correcting the moment of the floor reaction force about the desired central point of the floor reaction force and a position and posture of the robot so as to dynamically counterbalance the converted moment of the object reaction force; and joint displacing means for displacing joints of the robot based on the corrected moment of floor reaction force about the desired central point of the floor reaction force and the corrected position and posture of the robot.
The present invention is configured to have a system for controlling posture of a legged mobile robot having at least a body and a plurality of links each connected to the body, comprising: desired gait predetermining means for predetermining a motion pattern including at least a desired position of the body of the robot; object reaction force detecting means for detecting an object reaction force acting on the robot from an object through the links; object reaction force moment converting means for converting the detected object reaction force into a moment about a predetermined point; robot position/posture correcting means for correcting a moment of the floor reaction force about the predetermined point of a floor reaction force and a position and posture of the robot so as to dynamically counterbalance the converted moment; and joint displacing means for displacing joints of the robot based on the corrected moment of the floor reaction force about the predetermined point of the floor reaction force and the corrected position and posture of the robot.
It should be noted in the above that the xe2x80x9clegged mobile robotxe2x80x9d includes a legged mobile robot which is subject to the object reaction force through portions other than the arms. With respect to the arm links, it should also be noted that the arm links would include any links (including even the leg links) which act on an object. For example, if the robot is a insect-type robot with six legs which lifts an object using the two forelegs, the two forelegs should be considered as the arm links.